For an electrical connection between an electronic component such as a semiconductor element (IC chip) and the like and a circuit board, an anisotropic conductive connector has been widely used in recent years. As an anisotropic conductive connector, one prepared by dispersing conductive fine particles in an insulating film has been conventionally known. This anisotropic conductive connector is associated with problems of structurally difficult connection with a connection target having a fine pitch and the need for forming a terminal of the connection target, such as electrode of semiconductor element and the like in a protrusion (bump). Thus, as an anisotropic conductive connector capable of resolving such problems, namely, an anisotropic conductive connector capable of dealing with finely pitched and bumpless target, the Applicant of this invention has proposed an anisotropic conductive connector (film) comprising, in the substrate of an insulating film, plural conductive paths penetrating in the thickness direction of the film substrate while being insulated from each other, in international publication WO98/07216 (U.S. Pat. No. 6,245,175).
Generally, anisotropic conductive connectors have been employed for the following two uses. One is use as, what is called, a mounting connector, wherein an anisotropic conductive connector is disposed between an electronic component such as a semiconductor element and the like and a circuit board, which, upon heating and pressing, electrically and mechanically connects the electronic component and the circuit board. The other is use as, what is called, a test connector, wherein, in functional tests of electronic components such as semiconductor element and the like, an anisotropic conductive connector is inserted between an electronic component and a circuit board, which, upon press adhesion to the both, achieves a functionally testable conduction between the electronic component and the circuit board.
The use of an anisotropic conductive connector as a test connector is necessary because a functional test of an electronic component after mounting the electronic component on a circuit board only to prove that the electronic component is defective results in disposal of a good circuit board together with the component, thereby lowering the production efficiency of the circuit board and increasing an economical loss.
In a conduction test of a semiconductor element, an electronic component and a circuit board, a probe pin has been used conventionally, but a probe exclusive for each test subject component needs to be made because the position of an electrode differs for each test subject component. In recent years, moreover, the size of an electronic component and an electrode of a circuit board as well as distance between electrodes have been reduced, which makes production of a probe pin problematically difficult or costly. Thus, the use of an anisotropic conductive film has been proposed for conduction test of an electronic component and the like.
When an anisotropic conductive film is used as a test connector, a load for electric conduction between an electronic component and a circuit board is preferably as small as possible, in view of improved efficiency of test operation and prevention of terminal damage and deformation of an electronic component and a circuit board. To achieve this, an anisotropic conductive film is required to have flexibility permitting followability to the surface shape of an electronic component and a circuit board. On the other hand, when an anisotropic conductive film is used as a mounting connector, it is required to achieve not only easy contact of a conductive path of the connector to the terminal of a connection target such as an electronic component, a circuit board and the like, but also sufficient adhesion of the connector to a connection target.
As mentioned above, in order to enhance flexibility and adhesiveness of an anisotropic conductive film, it is preferable to increase the proportion of a resin in an anisotropic conductive film. However, the anisotropic conductive film proposed in WO98/07216 is produced by a method comprising winding an insulated conductive wire (metal wire coated with insulating resin layer) multiple times around a core, bonding coating layers to prevent separation from each other to give a winding block, and cutting this block in a desired thickness along the plane forming an angle with each insulated conductive wire (metal wire). Therefore, increase of the proportion of a resin in an anisotropic conductive film has been difficult. In other words, the thickness of an insulating resin layer of an insulated conductive wire cannot be increased beyond a certain level, and therefore, the proportion of a resin in an anisotropic conductive film cannot be increased sufficiently. Thus, the present Applicant has proposed, as a method for producing an anisotropic conductive film having a sufficiently increased proportion of a resin, a method comprising cutting out a film from a block having a multilayer structure achieved by alternately winding a layer of wound wire comprising an insulated conductive wire and an insulating resin film around a core (JP-A-2002-42921).